Method of producing a jet fuel

ABSTRACT

Jet fuel having a low freeze point, e.g. -50* F., and high heat of combustion per gallon, e.g. at least about 124,000 B.t.u./gal., is produced by blending (1) a highly naphthenic jet fuel component having an advantageously very low freeze point but low heat of combustion on a pound basis with (2) a highly paraffinic jet fuel component having a high heat of combustion on a pound basis in excess of that desired in the blended product.

United States Patent I 1 3,620,961

(72] Inventor Henry R. Ireland ISbI References Cited West DeptfordTownship, Gloucester UNITED STATES PATENTS County, NJ. y 1 pp No.796,687 2,910,426 /l959 bluesenkamp et a]. 208/66 3.367.860 2/1968Barnes ct al. u 208/ [22] PM 3 384 $14 5/1968 Halik ct al 208/15Patented Nov. 16, 1971 [73] Assignee Mobil Oil CorporationPrimary'ExaminerHerbert Levine Auornevs-Oswald G. Hayes Andrew L.Gaboriault and Carl D Farnsworth ABSTRACT: Jet fuel having a low freezepoint c.g F.. [54] a g R EZ AIET FUEL and high .heat of combustion pergallon e.g. at least about 6 2 124,000 B.t.u /gal., is produced byblending 1) a highly [52] US. Cl 208/79, naphthenic jet fuel componenthaving an advantageously very 208/15. 208/141, 208/216, 2081217 lowfreeze point but low heat of combustion on a pound basis [51] Int. ClC101 1/04 with (2) a highly paraffinic jet fuel component having a high[50] Field of Search .1 208/15, 17, heat of combustion on a pound basisin excess of that desired 79, 138, 141 in the blended product. I

F NAPHTHENIG FEED C T I 2 RAFF NAT 2 4 6 o KEROS'NE EXTRACTION E c NSTEP A T O R PARAFFIN FEED R so PRETREAT REFORMING ExTRAmN CH0 UDESULFURIZATION 2 SECTION STEP 7T METHOD OF PRODUCING A JET FUEL Thepresent invention relates to the production of jet fuel. Moreparticularly, this invention relates to the production of jet fuelshaving low freeze point and high energy content both on a weight basis(B.t.u./(b.) and on a volume basis (B.t.u./gal.).

As is well known, a jet fuel should have high-temperature stability,high energy content, and good handling characteristics at both low andhigh temperatures. An acceptable jet fuel must meet rather rigidspecifications for either military or commercial use. With the passageof time, these requirements have become more demanding. For militaryuse, there is a present need for an economical jet fuel which has a highenergy content per gallon in order to increase the operating range ofthe aircraft, and a lower freeze point than exhibited by most prior artfuels in order to improve in air refueling of the aircraft. By way ofexample, a new military jet fuel specification includes the followingrequirements:

Gravity, API 44-50 Freeze Point, 'F,, max, 46 Heat of CombustionB.t.u.llb., min. l8,700

B.t.uJgaL, min. l24,000 Luminometer Number, min. 75 Vapor Pressure,p.s.i.a. and 300 F., max. 3.0 Aromatics, vol. max. 5.0

Thermal Stability (300/500/600'BW F.)

Pressure Change, in Hg, max. 3 Preheater Deposit Code, max.

Thermal Precipitation Test the fuel must have a heat of combustion of atleast l24,000,

B.t.u./gal. eliminates many compositions which have the required heat ofcombustion on a pound basis. Fuels having a high A.P.l. gravity arecharacterized by less weight per gallon, and since the heat ofcombustion per gallon is based upon the weight per gallon together withthe number of B.t.u. per unit weight, a low A.P.l. gravity is desirablewith respect to obtaining high heat of combustion on a gallon basis. Onthe other hand, the heat of combustion per pound is ordinarily estimatedas the product of the A.P.l. gravity and the aniline number(aniline-gravity product) so that a reduction in the ART. gravity lowersthe number of B.t.u. per lb.

It is a primary object of the present invention to provide a novel jetfuel composition which is a blend of a naphthenic jet fuel componentwith a highly paraffinic jet fuel component, with the final producthaving desirable fuel properties which are intermediate between theproperties of the two individual components. The naphthenic componenthas a low freeze point and, when employed with a relatively high freezepoint paraffinic component, is used to lower the freeze point of theblended product. The naphthenic component is also used because it has ahigh volumetric heat of combustion. However, the naphthenic fuelcomponent has a low heat of combustion on a pound basis, below thatdesired in the final product. A presently preferred paraffinic fuelcomponent has a relatively high freeze point, and is employed primarilysince it has a heat of combustion on a pound basis in excess of thatdesired in the blended product. By blending a naphthenic component and aparaffinic component, it is possible to obtain a jet fuel compositionwhich will meet standards which could not be met by either thenaphthenic component alone or the paraffinic component alone or by minormodification of either component,

The relative amounts of the two components which are blended variessomewhat depending upon the properties of each component and theproperties desired in the final product. In general, the naphtheniccomponent and the paraffinic component are present in a volume ratio ofabout 35:65 to 60:40.

It is a further object of the present invention to provide a jet fuelcomposition having a freeze point of a maximum of about 46 F., a heat ofcombustion of at least about l8,700 B.t.u./lb., and a heat of combustionof at least about l24,000 B.t.u./gal.

In accordance with one embodiment of the invention, a naphthenic jetfuel component containing about 60 to 89 vol. percent naphthenes, about8 to 35 vol. percent paraffins, and less than about 5 voLpercentaromatics, and preferably less than about 3 vol. percent, is prepared byfractionating a highly naphthenic crude oil to obtain a kerosenefraction boiling in the range of about 380530 F., removing at least asubstan tial portion of the aromatic hydrocarbons from it, for exampleby sulfur dioxide extraction, hydrotreating the resulting relativelynonaromatic liquid in the presence of a hydrotreating catalyst to removesulfur and nitrogen compounds and olefins to thereby improve the thermalstability of the fuel, separating the resulting normally gaseous andnormally liquid fractions, to obtain the desired naphthenic jet fuelcomponent. This jet fuel component may be percolated through clay oralumina if desired. The naphthenic component is blended with aparaffinic jet fuel component processed in a particular manner andcontaining about 3-1 7 vol. percent naphthenes, up to about 5 vol.percent preferably, about 2-3 vol. percent aromatics, and the remainderbeing substantially paraffins. The paraffinic component has a heat ofcombustion of about l8,850l 8,960 B.t.u./lb. The paraffinic jet fuelcomponent is prepared by first desulfurizing a kerosene fractioncontaining at least about 40 percent (vol.) paraffins followed byreforming at a temperature in the range of about 790 to about 870 F.under conditions to dehydrogenate and isomerize naphthenes and toisomerize normal paraffins while maintaining at least 75 percentparaffin retention, separating the normally gaseous and normally liquidfractions from the reformate thus obtained, extracting at least asubstantial portion of the aromatic hydrocarbons from the liquidfraction in the reformate, for example, by sulfur dioxide extraction, toobtain a raffinatc comprising the paraffinic jet fuel component.

The naphthenic and paraffinic components processed substantially asabove described are blended to form a jet fuel composition having a heatof combustion greater than 123,000 B.t.u./9al., and preferably at leastabout 124,000 B.t.u./9al. and a heat of combustion on a pound basis ofat least about 18,700 B.t.u./lb., preferably at least 18,750 B.t.u./lb.,while maintaining a freeze point having a maximum of about 46 F.

FIG. 1 diagrammatically represents a simplified process flow arrangementfor preparing a jet fuel composition in ac cordance with the invention;

FIG. 2 is a graph illustrating the relationship between the A.P.l.gravity of the product and the heat of combustion of the product.

Referring now to the drawing, and more particularly to FIG. 1, apreferred embodiment of the invention will now be described.

PRODUCTION OF NAPHTHENIC FUEL COMPONENT The naphthenic fuel component ofthe jet fuel is prepared by fractionally distilling a suitable highlynaphthenic hydrocarbon charge in a fractionator to obtain for furtherprocessing a kerosene fraction boiling within the range of about 380 toabout 530 F. This naphthenic hydrocarbon charge should have a paraffincontent of less than about 35 vol. percent, and preferably in the rangeof about 5 to 30 vol. percent paraffins. Suitable feed stocks may be,for example, a mixture of three California crudes (Cal. mix), and astock known as Coastal A. To these may be added up to or vol. percent ofMurban, Four Corners, Alaskan or Qatar stocks. Other suitable naphtheniccharge stocks in the kerosene boiling range may also be employed.Suitable feed stocks have the following approximate composition andproperties.

Coastal A The kerosene fraction is passed from the fractionator to anextractor. in the extractor, the liquid fraction is contacted with asuitable solvent, for example, sulfur dioxide, which is selective forremoving aromatic hydrocarbons from the naphthenic charge. Theconditions employed during the solvent extraction are not unusual andconsidered substantially conventional by those skilled in the art. Thus,when employing liquid sulfur dioxide as the solvent, the sulfur dioxidemay be employed in a ratio of about 100 to about 300 vol. percent basedon the fraction being extracted, and the temperature may be in the rangeof about 20 to 50 F.

The raffinate from the extractor is then passed through a causticscrubber to remove residual sulfur dioxide, and then through a salttower considered a part of the extraction step to remove residualcaustic and water. It is then passed over a hydrogenation catalyst in aCHD unit where it is hydrotreated to improve its thermal stability byhydrogenation of olefins, if present, and effect removal of nitrogen andsulfur compounds and other impurities. For example, hydrogenation ofpyridine to ammonia and hydrogenation of thiophene to hydrogen sul fideis effected. The CHD hydrogenation is carried out in the presence of acatalyst which may be a known catalyst employed for treatment ofpetroleum fractions in order to hydrogenate olefins, tohydrodesulfurize, etc. Examples of such catalysts are Group V] and GroupVlll metals, oxides and sulfides, usually supported upon an inert porouscarrier such as activated alumina. Mixtures of Group VI and VIII metaloxides and sulfides are particularly advantageous. Exemplary catalystinclude cobalt molybdate and nickel molybdate on alumina which are theparticularly preferred catalysts of the invention.

The hydrogenation-desulfurization CHD treatment is carried out attemperatures between about 550 and about 750 F., preferably betweenabout 580-690 F., more preferably 625675 F. and at a space velocity ofup to 5.0, a hydrogen partial pressure of about 450 to 800 p.s.i.g., anda hydrogen recycle rate of about 500-3000 s.c.f./bbl. Although notillustrated on the simplified flow sheet, it will be understood that theproducts obtained from the hydrotreater are passed to a separator stepfrom which hydrogen rich gas is separated for recycle, preferably afterremoval of hydrogen sulfide and other impurities. After stripping offlight ends from the CHD treated naphthenic component, the normallyliquid fraction becomes the naphthenic high B.t.u./gal., low A.P.l.gravity component of the final jet fuel blend herein produced. In somecases, it may be desirable to also percolate this processed naphtheniccomponent through clay or bauxite or silica gel or mixtures thereofbefore blending it with the paraffinic component hereinafter describedto produce the final jet fuel product of this invention. The naphthenicjet fuel component thus prepared contains about 60 to 89 vol. percentnaphthenes, about 8 to 35 vol. percent paraffins, and preferably lessthan about 3 percent aromatics. It has a freeze point less than that ofthe freeze point desired in the final blended product and is usually inthe range of less than -76 to 60 F., preferably below 68 F. Thenaphthenic jet fuel component has a net heat of combustion of less thanabout l8,700 B.t.u./pound.

PRODUCTION OF PARAFFlNlC FUEL COMPONENT One function of the parafiinicjet fuel component comprising the jet fuel product herein described andproduced is to elevate the heat of combustion in B.t.u./lb. andluminometer number of the blended final product. Thus the paraffiniccomponent is prepared from selected petroleum hydrocarbon fractions ofthe kerosene type composed substantially of hydrocarbon mixtures boilingin the range from about 370 to about 550 F., preferably from about 380to about 530 F., and containing at least about 40 weight percentparaffins. Some specific suitable feed stocks include straight runkerosene fractions of the following compositions:

The kerosene fractions described above are usually initially subjectedto desulfurization and denitrogenation treatment prior to a lowtemperature mild catalytic refining or reforming treatment carried outunder particularly correlated reaction conditions in the presence of areforming catalyst having dehydrogenation and isomerizing activity suchthat the predominant reactions are dehydrogenation of naphthenes,isomerization of 5 carbon-ring to 6 carbon-ring naphthenes andisomerization of normal paraffins in the feed stock with at least 75percent paraffins retention; that is, cracking is minimized. Theresulting liquid reformate fraction after removal of gaseousconstituents generally boils within the same range as the feed and isthen solvent extracted to remove at least a substantial amount of thearomatics, which aromatics may be those originally present in the feedas well as those formed during the refining treatment, to provide asubstantially aromatic free raffinate constituting the paraffinic jetfuel component.

As provided above, the feed stocks may be treated prior to the reformingstep to remove sulfur and nitrogen impurities which would contaminatethe catalysts used in the reforming step and/or which would causecorrosion problems. Thus, feed stocks containing a relatively highconcentration of sulfur are preferably pretreated to reduce the sulfurconcentration to not more than about 50 parts per million, along withsubstantially complete removal, when present, of other undesirableimpurities including nitrogen, arsenic and lead. To effect this removal,the feed stock may be subjected to hydrodesulfurization by treatmentwith a suitable hydrodesulfurization catalyst (e.g. cobalt molybdate onalumina, nickel-tungsten sulfide, chromia on alumina etc.) in thepresence of hydrogen and conditions of pressure space velocity andtemperature to reduce the concentration of the aforementionedimpurities. The following conditions are illustrative of those suitablefor pretreatment of feed stocks of the invention and particularly fortreatment ofa 375-500 E. virgin kerosene from W. Texas crude employing acobalt molybdate hydrodesulfurization catalyst.

Space Velocity (LHSV) 2 Hydrogen Partial Pressure, p.s.i.g. 700

Temperature, F. hydrogen Circulation Rate (s.c.f./bbl.)

Space Velocity (LHSV) 0.5-l0

Hydrogen Partial Pressure 250-800 p.s.i.g.

Temperature, F. 600-800 Hydrogen Circulation Rate |90-3,000

Following the desulfurization pretreatment, the reaction products arepassed to a stripper where the gaseous phase rich in hdyrogen, andcontaining substantially all of the hydrogen sulfide and ammoniaproduced in the pretreater, is stripped from the liquid phase, forexample, by employing a stream of recycle gas from the reformer. Theliquid phase is then passed to a multistage reformer which isdiagrammatically shown in block form in FIG. I as having three stages.

In the reformer, the feed stock is subjected to mild catalytic treatmentunder correlated conditions to provide selective dehydrogenation of Cring naphthenes to aromatics, isomerization of alkyl C, ring naphthenesto C ring naphthenes which are then aromatized, and isomerization ofnormal paraffins to isoparaffins, while minimizing cracking. Theconditions are correlated to obtain at least 75 percent paraffinretention, and preferably at least about 95 percent paraffin retention.

The reformer treatment conditions can be varied depending upon theparticular feed stock employed, and upon the desired properties of theparaffinic fuel component to be produced, which properties arecorrelated with the properties of the particular naphthenic fuelcomponent which will be blended therewith to obtain the final blendedproduct. In general, the conditions are within the following ranges:

Space velocity (LHSV) 0.5-6 H,/feed, s.c.f.lbbl. 4,000-l0,000 AverageTemperature, F. 790-870 Hydrogen Pressure, .s.i. 300-800 In theillustrated embodiment in which the catalytic treatment is carried outin three stages, in the first stage, the feed stock is treated underconditions to effect substantial naphthene isomerization anddehydrogenation with only a nominal amount of other reactions such ascracking or isomerization of parafi'ins. The temperature of the feedentering the first stage may be about 870 F. while the temperature ofthe fraction leaving the first stage is in the order of 790 F. since thedehydrogenation reaction consumes heat. It will be understood thatreference to a three stage treatment is intended to include differentcatalytic reaction zones within a single reactor, or in separatereactors, each of which contains a catalyst (e.g. a bed of catalyst)with the reaction zones being interconnected by transfer lines for thepassage of product from one reaction zone to the other, which transferlines are equipped with heaters for heating the product from onereaction zone prior to its introduction into the succeeding reactionzone. In the second and third reaction zones, the conditions areregulated to achieve primarily isomerization of normal paraffins toisoparafins accompanied by some further dehydrogenation of anynaphthenes which may still be present. The feed to the second reactionzone may be heated to about 830 F., and the product leaving the secondreaction zone which may be at a temperature of about 810 F. ispreferably again reheated, for example, to about 820 F. beforeintroduction into the third reaction zone. The product from the thirdreaction zone may be at a temperature of about 810 F.

It will be understood that, for any given kerosene feed stock passed tothe reformer, as the average reaction temperature employed increasesfrom the lower to the higher. side of the stated temperature range, thespace velocities generally increase within the stated range. Inaddition, as the catalyst ages, the temperature is generally increasedat constant space velocity, or alternatively, the space velocity isdecreased while maintaining a substantially constant average temperaturein order to maintain a substantially constant quality of reformedproduct.

The catalyst employed in the reformer is a dehydrogenation catalysthaving selectivity for the isomerization and the dehydrogenation ofnaphthenes, and having low cracking activity.

For the catalytic treatment of the feed stocks embodied suitablecatalysts are metals of the platinum series and particularly, platinum,on carriers such as alumina. Specific examples thereof are catalysts, oflow cracking activity, comprising from about 0.1 to about 1.0 percentplatinum on alumina (e.g. eta alumina) or on a low-activitysilica-alumina base and which may contain a suitable halogen (e.g.chlorine) in an amount of up to about l.0 percent and, preferably, in anamount not greater than the platinum content, and preferably lower. Suchcatalysts that contain from about 0.3 to about 0.8 percent platinum areparticularly suitable. In a broader aspect, however, suitable for useherein are catalysts which, as is known to those skilled in the art,possess activity for dehydrogenating naphthenes to aromatics and are oflow cracking activity and, as further examples, such catalysts includetungsten and/or nickel on kieselguhr, chromium oxide on alumina, andothers.

The reformate is passed to an extractor for reduction of the aromaticconcentration, for example, by extraction with liquid sulfur dioxide.The conditions employed during the solvent extraction may besubstantially the same as those employed during the corresponding stepin treating the naphthenic jet fuel component, that is, when sulfurdioxide is the solvent, the sulfur dioxide may be employed in a ratio ofabout to about 300 vol. percent, based on the fraction being extracted,at a temperature in the range of about 20 to 50 F.

The paraffinic rafiinate obtained from the extraction step may besubjected to a relatively mild (CHD) hydrodesulfurization similar tothat discussed above with respect to the naphthenic componentpreparation and/or percolated through a suitable material to improve itsthermal stability and to yield the desired paraffinic jet fuel componentwhich also has found use 18,850-a relatively super jet fuel meetingdifferent specifications than those which are met by the blended productof the present application. Suitable percolation materials may be clay,bauxite, aluminas, silica gel and the like. The paraffinic jet fuelcomponent of the invention contains about 3-17 vol. percent naphthenes,a maximum of about 5 vol. percent, preferably about 2-3 vol. percentaromatics, and has a freeze point in the order of about 40 to 45 F. anda heat of combustion of about l8,850l8,960 B.t.u./lb.

Other suitable paraffinic blending components include a hydrogenatedheavy alkylate, and a paraffinic hydroisomerized product such ashydroisomerized wax or paraffinic hydrocrackate. The heavy alkylateblend stock is prepared by hydrogenating olefins in a heavy alkylatefraction boiling in the range of about 380550 F. employing processingconditions substantially the same as those described above for thehydrogenation and desulfurization of the naphthenic stock. These blendstocks have the advantage of having low freeze points. The properties ofthese blend stocks, and suitable hydrogenation conditions for thealkylate are set forth in the following table.

PROPERTIES OF PARAFFlNlC BLEND STOCKS 380-520 F. 37U-525 F. Heavy HydroAlltylate crackate LHSV, v m v bis-s.0 Temperature, Fv 550 750 ProductProperties Charge Product Product Gravity,APl 51.1 5l.l 52.4 AnilinePoint, Fv I96 I96 177.3 Luminometer No. 85 85 Heating Value, B.t.u./lb.l8,866 [8,864 [8,917

Freeze Point, F. 76 76 76 Composition, Vol. 5

Paraffins 85.0 87.0 87.2

Olefins 2.0 Naphthenes l2.0 l2.0 ll .0 Aromatics 1.8 L0 L8 The processflow arrangement of FIG. 1 above discussed provides several variationsin processing sequence which can be taken advantage of depending uponcontaminating materials found in the naphthene and paraffiniccomponents. Thus in one operating sequence of FIG. 1 herein identifiedas sequence A, the naphthenic product effluent of the CHD treating stepmay be passed by conduits 2, 4, 6 and 8 to a blending step wherein it isblended with a paraffinic product effluent of a separate CHD treatingstep found in conduit 22 and communicating with conduit 8 and theblending step.

On the other hand, in the preferred embodiment of FIG. I identified assequence B," the naphthenic product effluent of the naphthenic CHD stepand found in conduit 2 is combined with the paraffinic product componentin conduit 16 recovered from the paraffinic SO, extraction step. Thatis, the paraffinic product in conduit 16 may be passed through conduit20 containing valves 28 and 32 to conduit 14 containing valve 26 andcommunicating with the blending step by conduit 8 for blending with theabove identified naphthene product effluent in conduit 2. It is to benoted that the paraffinic product in conduit 20 is preferably firstpassed through a clay or alumina percolation step 38 by way of conduit34 containing valve 36 and the percolated product is then passed byconduit 40 containing valve 42 to conduit 20 and then to conduit 14.When employing the percolation step, valve 32 in conduit 20 will beclosed.

In another embodiment, identified as sequence C, the naphthenicraffinate of an extraction step found in conduit 10 is passed byconduits l2 and 20 to be combined with the paraffinic raffinate of aseparate extraction step found in conduit 16. The combined raffinatesare then passed to conduit 18 containing valve 30 to CHD treatmentbefore being recovered or passed to the blending step by conduits 22 and8.

In still another arrangement, identified as sequence D, the paraffinicproduct recovered from the percolation step by conduit 40 may becombined with the naphthenic raffinate found in conduit 12 which may ormay not have been percolated and the mixture thus formed passed to theblending step by way of conduits l4 and 8.

It is to be noted that the several different processing sequences abovebriefly outlined as sequences A," B," C" and D" are available for usewith particular charge materials depending upon the extent of undesiredcontamination found in the respective paraffinic and naphtheniccomponents after the aromatic removal steps. While one sequence oranother may offer some economic advantage over another for particularcharge material, sequence B" is preferable to the others for handling avariety of charge stock materials with a maximum of versatility. Thussequence "B" is the preferred embodiment of this invention since itprovides the versatility above referred to, permits operating thenaphthenic charge CHD treating step at a lower temperature and thesequence provides a greater thermal stability to the product as measuredby the TPT test.

BLENDING OF NAPHTHENIC AND PARAFFlNlC COMPONENTS In order to achieve ablended jet fuel composition having desired properties, the naphthenicjet fuel component and the paraffinic jet fuel component are blended ina volume ratio of between about 35:65 to 60:40, and where it is intendedto meet the aforementioned military specifications including the heat ofcombustion of about 124,000 B.t.u./gal., these components are blendedwithin the aforementioned ranges to give a product having a gravity ofabout H5.5 to 470 A.P.l.

Furthermore to make the specification of 18,700 B.t.u./lb., the blendedjet fuel should have a paraflin content between 50-62 vol. percent.About 50 vol. percent paraffins will make the specification when theamount of aromatics is about 2 vol. percent, this being a typicalmaximum aromatic content following sulfur dioxide extraction. A paraffincontent of about 62 vol. percent will make the specification when thearomatics content is at its maximum permissible value of 5 vol. percent.ln addition, at least about 50 vol. percent paraffins is required in theblended jet fuel in order to give a luminometer number of 75 or betteras required by the specifications.

Referring to FIG. 2, it may be seen that to make the two heat ofcombustion specifications, it is necessary to operate above the 18,700B.t.u./lb. line and to the left of the 124,000 B.t.u./gallon line.However, for the blended product to have the necessary composition, thegravity must be maintained between the narrow limits of H55 to 470A.P.l. and preferably 460 to 470 A.P.l. To meet the restrictions aboveidentified, it is immediately clear that it is necessary to operatewithin the shaded area shown on E16. 2.

In addition to providing the product with a freeze point of -46 F. orless, the components should be blended to provide a product having amaximum of about 18 percent normal paraffins. It will be appreciatedthat, in addition to adjusting the relative amounts of the twocomponents, the normal paraffin content of the paraffinic component maybe varied by way of the treatment of the paraffinic component in thereformer to isomerize normal paraffins.

It will also be appreciated that, within permissible specificationslimits, known jet fuel additives may be combined with the blendedproduct. Such known additives include oxidation inhibitors and metaldeactivators.

The invention will be more specifically described with reference to thefollowing examples.

EXAMPLE 1 A naphthenic fuel component is prepared by introducing Cal.mix, the mixture of three California crudes as described into afractionator and recovering a kerosene fraction boiling within the rangeof 380-530 F. The kerosene fraction is passed to an extractor wherearomatics are removed by sulfur dioxide extraction employing a ratio ofsulfur dioxide of 250 vol. percent based on the fraction being extractedand a temperature of 4 F. The raffinate from the extractor is passed toa CHD reactor where it is hydrotreated at a hydrogen pressure of 650p.s.i.s., a LSHV of 2 v./hr./v., a hydrogen circulation rate of 500s.c.f./bbl, and a temperature of 625 F., in the presence of a cobaltmolybdate desulfurization and denitrogenation catalyst. The normallyliquid fraction thus treated is percolated through clay and thenrecovered as the naphthenic component of the jet fuel blend.

A paraffinic fuel component is prepared from a straight run kerosenefraction which is pretreated as by desulfurization to remove impuritiesat a hydrogen pressure of 700 p.s.i.a., a LHSV of 2.0, a hydrogencirculation rate of 2,000 s.c.f./bbl, a temperature of 700 F., and inthe presence of a cobalt molybdate hydrodesulfurization catalyst. Afterseparation and removal of the gaseous phase in a stripper, thedesulfurized normally liquid fraction is passed to the first of athree-stage reformer wherein dehydrogenation of naphthenes andisomerization of paraffins is carried out with only nominal amounts ofother reactions such as cracking. The feed enters the first stage of themultistage reformer at a temperature of 870 F. and leaves at 790 F.After reheating to 830 F., the feed passes to the second zone from whichit exits at 810 F., and is reheated to 820 F., for introduction into thethird and last stage from which the product leaves at 810 F. Theeffluent of the reforming step is separated to recover a gaseous phasefrom the normally liquid reformate product. The normally liquid productfrom the reformer is passed to an extractor where aromatics are removedby sulfur dioxide extraction employing sulfur dioxide in a ratio of 250vol. percent based on the fraction being extracted, at a temperature of4 F. The raffinate is then percolated through bauxite to improve itsthermal stability and the desired paraffinic jet fuel component is thusobtained.

The naphthenic and paraffinic components are then blended to produce ablended jet fuel composition.

The properties of three blended jet fuel compositions prepared byblending naphthenic and paraffinic components as described above are setforth in the following table.

BLENDED JET FUEL COMPOSITIONS Components Blend 1 Blend 2 Blend 3Paraffinic component 56.5 58.5 62

vol. Naphthenic component 43.5 41.5

vol. I: Topped Naphthenic component 38 vol. b Properties Gravity, API46.6 46.6 46.6 Aniline Point, 'F. 170.0 170.5 172.3 Total Absorption,vol. I: 2.6 3.3 30 Heating Value B.t.u.l|b. (AXG) 18,753 18,755 18,765B.t.u./lb. (calorimeter) l8,770 18,760 18,780 B.t.u./gal. 124.050124,060 124,130 Freeze Point, 'F. -51 51 50 Freeze Point of ParaffinicComponent 'F. 40 40 -45 Freeze Point of Naphthenic Component F. -70 68-60 Distillation, ASTM, 'F.

117p. 370 377 411 I 409 405 421 20 41B 411 424 so 433 426 437 70 447 441449 90 476 470 476 EP 5 14 502 515 *Before blending, the naphtheniccomponent was topped.

One of the more severe tests of the specification for this fuel is theThermal Precipitation Test. This test, designated P&WA-MCLQ67 by thePratt and Whitney Aircraft Corporation has the purpose of heating thefuel to be tested at a specified rate to 300 F., digesting the fuel at300 F. for 2 hours, cooling the fuel at a specified rate, anddetermining by filtration if this heat treatment has causedprecipitation on insoluble matter. The details of the test are asfollows.

THERMAL PRECIPITATION TEST OF JET FUEL INSOLUBLES 1. Apparatus A. FuelPreconditioning Unit including Fuel Reservoir and ReservoirAssemblyModel No. 2200, Erdco Engineer ing Corp. Unit shall be capableof maintaining fuel at 300 F. i F.

B. Vacuum Pump-free air capacity 33.4 liters per minute,

Model No. I406-H, Welch Mfg. Co., or equivalent.

C. Fuel Filtration Unit-Model XX 2004720, Millipore Corp.

D. Oven-capable of maintaining a temperature of 180 F.

E. Filtering Flask-4,000 ml.

11. Materials A. Filter Paper-0.45 micron pore size, 47 mm. diameter,

Type HA, Millipore Corp.

B. Precipitation Naptha-Conforming to ASTM D9l-6l,

prefiltered through 0.45 micron filter paper.

C. Aluminum foil.

D. Lint free clothConsolidated Electrodynamics Corp.,

PIN 18560 or equivalent.

E. PWA 523 Fuel Thermal Precipitation Color Standard.

F. Pentane-prefiltered through 0.45 micron filter paper.

G. Petri Dish-Millipore Corp., P/N PD 1004700.

111. Procedure A. Preparation of Test Filter Papers I. With forceps,place filter paper in the precleaned fuel filtration unit and assembleunit with filtering flask and vacuum pump. Start pump.

2. Decant three 25 ml. increments of naphtha into filtration unit. Alloweach increment to filter completely through filter paper before addingthe next increment.

3. Turn vacuum pump off and relieve vacuum in filtration unit.

4. With forceps, carefully remove filter paper from filtration unit andplace in 180 F. 15 F. for 30 minutes.

5. With forceps, remove filter paper from oven and place in Petri dish.Close dish.

B. Preparation of Filtering Flask and Fuel Reservoir l. Flush filteringflask with 200 ml. naphtha.

2. Air dry the filtering flask.

3. Flush fuel reservoir with 400 ml. naphtha.

4. Dry the fuel reservoir interior by wiping with a lint free cloth orwashing with pentane and allowing to air dry.

C. Preparation of Test Fuel and Heating Cycle Operation 1. Filter 3gallons of test fuel through filter paper according to step A1. Discardfilter paper.

2. Refilter the fuel through another filter paper. Discard filter paper.Cover fuel filtration unit with aluminum foil.

3. Place test fuel in precleaned fuel reservoir exercising care toprevent the inclusion of airborne matter.

4. Assemble reservoir assembly being careful to check and tightenwater-cooling coil.

5. Close Water lnlet Valve.

6. Turn Main Power Switch On.

7. Turn Heater Selector Switch to Medium.

8. Set Temperature Controller to 300 F. Temperature of 300 F. shall beattained in l00 to 20 minutes.

9. Maintain temperature at 300 F. :5" F. for 120 minutes.

10. After lZO-minutes heating cycle, turn Heater Selector Switch to Off.

11. Open Water Inlet Valve. The fuel temperature shall drop to F. i5 F.in 30 to 45 minutes.

12. When fuel has cooled to 80 F. 15 F., close Water lnlet Valve.Disassemble fuel reservoir.

l3. Cover open reservoir with aluminum foil.

D. Filtration of Test Fuel 1. With forceps, place the prepared filterpaper from A5 in the precleaned filtration unit and assemble unit withfiltering flask and vacuum pump. Start pump.

2. Filter 3,785 ml. (1 gallon) of the fuel from C13 within 1 hour usinga graduated cylinder taking care to prevent airborne contamination.Note: Covering the filtration unit and graduated cylinder with aluminumfoil during filtration is acceptable.

. Wash the filter paper and inside walls of filtration unit with three25 ml. increments of naphtha. Allow each increment to filter completelythrough filter paper before adding the next increment.

. Repeat steps A3 through A5.

. Compare colors of sample and Color Standard and report the test asdarker, equal to, or cleaner than the standard.

The jet fuel blend was tested in the Thermal Precipitation Test (TPI)and it passed that test with the very good rating Shell code rating 1.Shell code rating 1 corresponds to a pass in the P&W rating system. AShell code rating of 2 or greater corresponds to a fail in the P&Wsystem.

EXAMPLE 2 The same naphthenic jet fuel component as that of example 1was prepared by introducing Cal. mix, the mixture of three Californiacrushes as described previously, into a fractionator and recovering akerosene fraction boiling within the range of 380-530 F. The kerosenefraction thus obtained was passed to a CHD reactor where it washydrotreated at a hydrogen pressure of 650 p.s.i.a., a LHSV of 2v./hr./v., a hydrogen circulation rate of 500 s.c.f./bbl., a temperatureof 625 F., and in the presence of the same cobalt molybdate catalyst ofexample 1. The normally liquid fraction is recovered and passed to anextractor where aromatics are removed by sulfur dioxide extractionemploying a ratio of sulfur dioxide of 250 vol. percent based on thefraction being extracted and a temperature of 4 F. The raffinate fromthe extractor is then percolated through clay to obtain the desirednaphthenic jet fuel component. This naphthenic component is then blendedwith the same paraffinic component as that of example I to produce ablended jet fuel composition.

This jet fuel blend was tested in the Thermal Precipitation Test and itfailed that test with a rating of Code 2-3.

EXAMPLE 3 The same naphthenic component as that of examples I and 2 wasCHD-treated, So -extracted and percolated in that sequence as in thecase of example 2 except that the CHD conditions were 650 p.s.i.a., aLHSV of l v./hr./v., a hydrogen circulation rate of 1,000 s.c.f./bbl.,and a temperature of 650" F. The naphthenic component thus treated wasblended with the paraffinic component in the same way as example 2. Thisjet fuel on TP Testing was rated as a Code 1-2 borderline failure. Thiswas the best rating achieved in a series of tests in which the Cal. mixkerosene was treated at varying CHD conditions followed by aromaticsextraction and percolation.

The significant differences between examples I and 2 are as follows: Inexample 1, SO, extraction preceded CHD treatment and in example 2, SO,extraction followed CHD treatment. Thus, the comparison of examples 1and 2 shows that aromatics extraction before CHD hydrogen treatmentproduces a jet fuel blend having a better TPT rating than the reversesequence represented by example 2. in addition, the comparison betweenexamples I and 3 shows that using the sequence of aromatics extractionbefore CHD hydrogen treatment permits obtaining good TPT ratings usinglower temperatures and hydrogen circulations in the hydrogen treatmentstep than in the case of hydrogen treatment before aromatics extraction.

EXAMPLE 4 A naphthenic fuel component is prepared by introducing Cal.mix, the mixture of three California crudes as described previously inadmixture with four corners crude in a minor amount, into a fractionatorand recovering a kerosene fraction boiling within the range of 380-530F. The kerosene fraction is passed to an extractor where aromatics areremoved by sulfur dioxide extraction employing a ratio of sulfur dioxideof 250 vol. percent based on the fraction being extracted and atemperature of F. The raffinate from the extractor is passed to a CHDreactor where it is hydrotreated at a hydrogen pressure of 650 p.s.i.a.,a LHSV of 1.3 v./hr./v., a hydrogen circulation rate of l,500s.c.f./bbl., a temperature of 645 F., in the presence of a cobaltmolybdate desulfurization and denitrogenation catalyst. The normallyliquid fraction thus treated is recovered as the naphthenic component ofthe jet fuel blend.

A paraffinic fuel component is prepared from a straight run kerosenefraction which is pretreated as by desulfurization to remove impuritiesat a hydrogen pressure of 700 p.s.i.a., a LHSV of 2.0, a hydrogencirculation rate of 2,000 s.d.f./bbl., a temperature of 700' F., and inthe presence of a cobalt molybdate hydrodesulfurization catalyst. Afterseparation and removal of the gaseous phase in a stripper, thedesulfurized normally liquid fraction is passed to the first of athree-stage reformer wherein dehydrogenation of naphthenes andisomerization of paraffins is carried out with only nominal amounts ofother reactions such as cracking. The feed enters the first stage of themultistage reformer at a temperature of 870 F. and leaves at 790 F.After reheating to 830 F., the feed passes to the second zone from whichit exits at 8l0 F., and is reheated to 820 F., for introduction into thethird and last stage from which the product leaves at 8 [0 F. Theeffluent of the reforming step is separated to recover a gaseous phasefrom the normally liquid reformate product. The normally liquid productfrom the reformer is passed to an extractor where aromatics are removedby sulfur dioxide extraction employing sulfur dioxide in a ratio of 250vol. percent based on the fraction being extracted, at a temperature of10 F. The raffinate is then percolated through clay to improve its thermal stability and the desired paraffmic jet fuel component is thusobtained.

The naphthenic and paraffinic components are than blended to produce ablended jet fuel composition having an A.P.l. gravity of 46.3. Theproperties of this jet fuel composition are shown in table I.

TABLE 1 Test Test Results Gravity,'APl 46.3 Distillation Temperature, F.

Initial Boiling Point 383 10% Evaporated 407 20% Evaporated 4l0 50%Evaporated 434 Evaporated 48l End Point 522 Residue, Vol. I: L0 LossVol.% L0 Existent Gum, mg.ll00 ml. 0.4 Total Potential Residue, l6 hr.aging,

mgJlOO ml. 0.5 Sulfur, wt. 0.02 Mercaptan Sulfur, wt. 0.000l Aromatics,vol. 1.8 Flash Point, F., PMCC I58 Freezing Point, F. 50 Copper StripCorrosion, 2hr.at2l2F. l

Net Heat of Combustion B.t.u./lb. 18,735 B.t.u./gal. l24,l38 LuminometerNo. 87 Water Reaction, Interface Rating lb Water Separometer IndexModified 94 Thermal Stabilit'y: CRC Fuel Coker (300/500/600) PressureChange, Inches Hg 0.6 Preheater Deposit Code 2 Vapor Pressure, p.s.i.a.

at 300 F. 2.65 at 500 F. 44.0 Thermal Precipitation Test- PdrWA-MCLQ 67Pass Fuel System Icing Inhibitor, vol. l: 0.1 l Particulate Matter,mgJgal. 0.5

It is to be noted from table I that this blended jet fuel product passedthe Thermal Precipitation Test (TPT) with a rating of Code 1.

Having thus provided a general description of the improved method andcombination of processing steps to be practiced by this invention andprovided examples in support thereof, it is to be understood that noundue restrictions are to be imposed by reason thereof.

lclaim:

l. A method for producing a jet fuel product having a heat of combustionequal to or greater than 124,000 B.t.u./gal. and 18,700 B.t.u./lb. whichcomprises (a) processing a naphthenic rich charge boiling from about 380to about 530 F. through the combination of aromatic extraction followedby catalytic hydrodesulfurization so as to produce a naphthenicjet-fuelboiling component containing less than 35 vol. percentparaffins, volume percent aromatics and 50 p.p.m. of sulfur, (b)processing a paraffin rich charge material boiling in the range of 370F. to about 550 F. comprising at least about 40 vol. percent paraffins,and less than 50 p.p.m. of sulfur by catalytic reforming underisomerizing conditions to maximize paraffin retention, and produce afterextraction of aromatics therefrom a reformed paraffinic jet fuelcomponent containing less than about 17 vol. percent naphthenes and lessthan 5 vol. percent aromatics which will produce upon selected blendingwith the above naphthenic component, (c) a jet fuel product blend havinga gravity in the range of about 45.5 to about 47 A.P.l., and a paraffincontent in excess of about 50 vol. percent.

2. The method of claim I wherein the naphthenic component is blendedwith the paraffinic component in a volume ratio between about 35:65 toabout 60:40.

3. The method of claim 1 wherein the paraffin rich reformate componentrecovered after removal of aromatics therefrom is blended with thenaphthenic component after aromatic removal and the blend thus formed isthen hydrogenated to remove undesired sulfur constituents.

4. The method of claim 1 wherein the naphthenic jet fuel charge materialis blended with the paraffin rich jet fuel reformate product beforetreatment to remove aromatic and sulfur bodies.

5. The method of claim 1 wherein the parafi'inic jet fuel componentrecovered from the aromatic removal step is percolated through a solidadsorbent material before blending with the hdyrogenated naphthenic richjet fuel component.

6. A method for producing ajet fuel product having a heat of combustionequal to or greater than l24,000 B.t.u./gal. and an A.P.l. gravity inthe range of 45.5 to 47 which comprises (a) processing a naphthenic richcharge containing less than 35 vol. percent paraffins and boiling in therange of 380 to 530 F. by the steps of aromatic removal followed byhydrogenation thereof sufficient to remove sulfur bodies to at leastabout 50 ppm. to form a naphthenic product material containing fromabout 60 to about 89 vol. percent naphthenes, (b) processing adesulfurized paraffin rich jet fuel boiling range material throughcatalytic reforming under conditions to efiect dehydrogenation ofnaphthenes, isomerization of C carbon ring and C carbon ring naphthenesand isomerization of n-paraffins to produce a paraffin rich jet fuelproduct which will have after removal of aromatics a heat of combustionin the range of about l8,850 to about l8,960 B.t.u./!b. and a freezepoint of the order of about -40 to about --45 and (c) blending thenaphthenic product material with the above produced paraffin rich jetfuel product in a volume ratio selected to produce a blended jet fuelproduct in a volume ratio selected to produce a blended jet fuel producthaving a paraffin content above 50 vol. percent and a heat of combustionequal to or greater than 18,700 B.t.u./lb. and an A.P.l. gravity in therange of 46 to 47.

i t B UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION DatedJanuary 3, 1972 Patent No. 3,

Inventor(s) HENRY R. IRELAND It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Abstract,

Column Column Column Column Column Column Column Column Column ColumnColumn Column Column Column Column Column (SEAL) Attest:

EDWARD M.PLETCHER,JR.

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line Ml After "/6oo delete "13w" "Btu/ sl should be --Btu/gallon--"Btu/9gal" should be --Btu/gallon-- "500E" should be --500F- After "use"delete --l8,850-- After "18,850" insert "11.0" should be under "Product"column "HF.5" should be 45.5"

"111 .5" should be +5.5--

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"lh should be 1132-- should be 11" is; not in exact position under colu"15F" insert --oven- J to 20" should be "100 to Signed and sealed this6th day of June 1972.

Attesting Officer ROBERT GOTTSCIIALK Commissioner of Pate

2. The method of claim 1 wherein the naphthenic component is blendedwith the paraffinic component in a volume ratio between about 35:65 toabout 60:40.
 3. The method of claim 1 wherein the paraffin richreformate component recovered after removal of aromatics therefrom isblended with the naphthenic component after aromatic removal and theblend thus formed is then hydrogenated to remove undesired sulfurconstituents.
 4. The method of claim 1 wherein the naphthenic jet fuelcharge material is blended with the paraffin rich jet fuel reformateproduct before treatment to remove aromatic and sulfur bodies.
 5. Themethod of claim 1 wherein the paraffinic jet fuel component recoveredfrom the aromatic removal step is percolated through a solid adsorbentmaterial before blending with the hdyrogenated naphthenic rich jet fuelcomponent.
 6. A method for producing a jet fuel product having a heat ofcombustion equal to or greater than 124,000 B.t.u./gal. and an A.P.I.gravity in the range of 45.5 to 47 which comprises (a) processing anaphthenic rich charge containing less than 35 vol. percent paraffinsand boiling in the range of 380* to 530* F. by the steps of aromaticremoval followed by hydrogenation thereof sufficient to remove sulfurbodies to at least about 50 p.p.m. to form a naphthenic product materialcontaining from about 60 to about 89 vol. percent naphthenes, (b)processing a desulfurized paraffin rich jet fuel boiling range materialthrough catalytic reforming under conditions to effect dehydrogenationof naphthenes, isomerization of C5 carbon ring and C6 carbon ringnaphthenes and isomerization of n-paraffins to produce a paraffin richjet fuel product which will have after removal of aromatics a heat ofcombustion in the range of about 18,850 to about 18,960 B.t.u./lb. and afreeze point of the order of about -40 to about -45 and (c) blending thenaphthenic product material with the above produced paraffin rich jetfuel product in a volume ratio selected to produce a blended jet fuelproduct having a paraffin content above 50 vol. percent and a heat ofcombustion equal to or greater than 18,700 B.t.u./lb. and an A.P.I.gravity in the range of 46 to 47.